1. Technical Field
This invention relates to a data recording method used in an apparatus for recording information onto an optical disk by emitting a laser beam to the optical disk.
2. Related Art
Recently, optical disks have become highly desired to be used for visual application, and thus it is desired that optical disks be capable of mass storage and be able to be accessed at a high speed. For this purpose, there needs to develop an art capable of recording more microscopic information. Further, it is important to reduce an overhead region which is a portion that does not directly contribute to the capacity such as an address region.
FIG. 10 is a view illustrating a physical sector structure on a track of a conventional optical disk. As shown in FIG. 10, the optical disk has a sector 901 which includes an address region 902 indicating address information and a data region 903 to/from which information can be recorded/reproduced. The data region 903 is located in both a groove track 904 and a land track 905 between the groove tracks. The address region 902 includes a header region 906 and a mirror region 907. The header region 906 is used to record concavo-convex pits which are produced when the optical disk is manufactured, and can not be re-written.
FIG. 11 shows a sector format. As described above, the sector includes the address region 902 and the data region 903. The address region 902 includes a header region 906 of 128 bytes and a mirror region 907 of 2 bytes. The data region 903 includes 2418 bytes of user data region 1007 used to record user data, 68 bytes of clock extraction region 1006, and 81 bytes of buffer region 1008. The clock extraction region 1006 is used for a PLL (Phase Locked Loop: to generate a clock with frequency and phase locked to an input signal) to input the signal for extracting the clock at data reproduction, and is used to absorb a deterioration of a front portion caused by iterative data recording. The buffer region 1008 is used to absorb a position shift at data recording or a deterioration of an end portion caused by repeated data recording.
To record 2418 bytes of data in the user data region of one sector, the above described optical disk needs 128 bytes of header region, 2 bytes of the mirror region, 68 bytes of clock extraction region, and 81 bytes of buffer region. Accordingly, 2697 bytes length in total is needed for a sector. The data portion includes a portion for error correction, and therefore a sector needs 2697 bytes length to store 2048 bytes of data. At that time, a utilization ratio of the disk (format efficiency) for recording a signal on the disk is 75.9% (=2048/2697). This means that the format includes 24.1% of redundancy.
For example, in order to record 4.7 GB of data, more data has to be recorded on a unit area with 75.9% of format efficiency than that needed in the recording with 100% of format efficiency. The quality of reproduction signal with 75.9% of format efficiency deteriorates less than that with 100% of format efficiency. To reduce the redundancy, there is a method to reduce a length of the clock extraction region 1006 in the data region. However, this method causes a problem that it becomes difficult to extract the clock used for data reproduction operation in PLL in a front portion of a series of data.